The invention relates to an ion barrier layer on metals and nonmetals (particularly polyolefins), and to a method for its production.
It is known that nonmetals serve as suitable insulating materials on metallic conductors of electric current because of their extremely low electroconductivity. The insulating properties of these nonmetals are impaired by in-diffusion of metal ions from the conductor material, particularly by the in-diffusion of heavy metal ions. However, these nonmetals also undergo a structural degradation due to catalytic reactions which are triggered by the in-diffusing metal ions. The catalytic reactions intensify at elevated temperatures and the nonmetals are thereby severely damaged or even destroyed. Ions of the heavy metals, such as copper, silver, nickel, cobalt, manganese, and their alloys, are particularly destructive, causing depolymerization reactions and oxidative degradation of polyolefins nonmetals such as polyethylene, polypropylene, and their copolymers.
On the other hand, nonmetal ions, particularly oxygen and sulfide ions, can also create a problem. These ions are able to penetrate through nonmetal layers, for example, layers of plastics such as polyolefins, and thereby chemically attack the heavy metal surfaces to form, for example, oxides or sulfides of the metals. The oxides or sulfides can invade the nonmetals and bring about adverse changes by initiating chemical structural alterations. The purely mechanical bond between metal and nonmetal (i.e., between conductor metal and nonconductor layer) is loosened and broken as a consequence. The electrical properties of metallic conductors are thereby reduced, and consequently, their use and practical value are impaired or rendered uncertain.
The prior art has attempted to avoid such damage and defects by placing relatively thick, and hence expensive, intermediate layers of tin or nickel between the conductor metal and the non-conductor, or, by mixing certain inhibitor substances into the polyolefins which bind the metal ions and eliminate or abate their harmful effect. In most cases, however, additives of these or other types adversely affect the quality of the electrical and mechanical properties of the insulating materials and effect only a partial solution to the problem. Sufficient protection could not be obtained, especially at elevated service temperatures of the insulated conductor.
From the European patent application published under number 0 044 668, it is known to employ aluminum foils as oxygen ion barriers. The aluminum foils should have a thickness of more than 15.mu.m, preferably 20.mu.m. According to the embodiment example, the aluminum foil is 25.mu.m thick. Wrapping and gluing are necessary steps. As to process technology, the cladding of the conductor with metal foil must be gapless, which is expensive and difficult to realize.
It is an object of the present invention to protect components and shaped parts of metals and nonmetals (particularly of plastic, such as polyolefins) against in-diffusing metal ions and to prevent the accompanying thermocatalytic degradation which is brought about by such in-diffusion, particularly by the heavy metal ions of copper, silver, nickel, cobalt, manganese, and their alloys while at the same time avoiding the chemical attack on metals and metal alloys caused by in-diffusing nonmetal ions, particularly oxygen and sulfide ions.